The present disclosure relates generally to semiconductor manufacturing and, more particularly, to a method and apparatus for thinning a substrate.
In semiconductor technologies, a silicon substrate may be employed and may undergo various processes to form active and passive devices therein. One such process includes thinning the substrate by various techniques such as grinding, chemical mechanical polishing (CMP), and etching. For example, backside-illuminated (BSI) image sensor devices are used for sensing a volume of radiation (e.g., light) projected towards the back surface of a substrate. To do this, an image sensor device uses an array of image sensor elements (e.g., pixels). Each image sensor element includes at least one radiation sensing element, described herein, as a photodetector. The photodetectors may be formed on the front side of the substrate, and then a face to face (e.g., front side to front side) bonding with a carrier (support) material may be performed to avoid the risk of device wafer warping following thinning, the substrate being thin enough to allow the radiation incident on the back surface of the substrate to reach the photodetectors. A thin substrate may be advantageous in reducing optical and/or electrical cross-talk between image sensor elements. Thinning the substrate from the back surface involves grinding the substrate and etching the substrate. However, it may be difficult to control an etch rate due to the highly reactive chemicals that are used to etch the substrate. Further, the surface topography of the substrate after etching may not be uniform due to various factors such as different etch rates at different areas on the substrate and the fierce chemical reactions of the etching process. This can adversely affect subsequent processes such as depth of focus (DOF) in photolithography and device optical performance such as sensitivity and cross-talk.
Therefore, what is needed is an improved method and apparatus for thinning a semiconductor substrate.